CHAPTER – 5
Growth
Definition
The process in which a permanent increase occurs in the body of plant
in respect to its size, form, weight and volume is called Growth.
OR
A permanent irreversible increase in size, weight, shape and structure
is called Growth.
Example
A new born becomes
mature when it is passed through growth.
Development
Definition
The study of a process of progressive changes through which a
fertilized egg passes before it assumes an adult form is called Development.
OR
The process of progressive changes in which the fertilized egg is
changed into a multicellular adult organism is called Development.
Embryology Or Development Biology
The study of
developmental changes from egg to adult stage is called embryology or
developmental biology.
Growth and Development in Plant
Definition
In higher plants, the entire plant body is not capable of growing but
growth is limited to certain regions known as Growth Points.
Meristem
Definition
Growth points consists of groups of cells which are capable of
division, these growing points are called Meristem.
Meristem Cell
Meristem consists of group of cells which are capable of division and
giving rise to new cells. These dividing cells are called meristematic cell.
Location
These meristematic cells are located at the stem and root.
Types of Meristem
There are three type of meristem
i. Apical Meristem
ii. Intercalary Meristem
iii. Lateral Meristem
i. APICAL MERISTEM
Definition
The meristem which is responsible for primary growth is called as
Apical Meristem.
Location
The apical meristem
are found at the tips of root and shoot.
Functions
§ Due to their activity, primary structures are formed.
§ They are responsible for the production of branches, leaves,
flowers and root hairs.
ii. INTERCALARY MERISTEM
Definition
The meristem which is considered as a portion of apical meristem but
separated by permanent tissues and it is of temporary nature called Intercalary
Meristem.
Location
They are found at
the base of internode, mint and also in other plants at the base of leaves.
Functions
§ Increase in length also takes place by activity of intercalary
meristem.
§ It play important role in the production of leaves and flower.
iii. LATERAL MERISTEM
Definition
The meristem which is responsible for the secondary growth is called
Lateral Meristem.
Location
They are found in
gymnosperms and dicot plants. These are composed of cambium and phalogen
tssues. They are present in vascular bundle or between them and also beneath
the epidermia.
Structure
Lateral meristem
are cylindrical in structure.
Functions
§ They increase the diameter of stem and roots.
§ They formed secondary tissues.
Phases of Growth
Growth of
multicellular plant is divided into three phases
1. The formative
phase
2. Elongation phase
3. Maturation phase or differentiation phase
1. The Formation Phase
§ It occurs at the tip of root and shoots.
§ During this phase, cell constantly divides and thus increases
their number by mitosis.
§ In this phase cells are closely packed together.
§ The cells having thin cellulose walls, dense cytoplasm and large
nuclei in this phase.
2. Elongation Phase
§ This phase occur immediately behind the formative phase.
§ During elongation phase, the cells volume increases due to
osmosis (uptake of water) and salt entrance.
§ It increases the turgor pressure and their thin elastic wall is
expanded.
§ Synthesis of new cytoplasm and cell wall proceeds on.
§ The cell enlarges and elongate until they reach their maximum
size.
§ In the root, the region of elongation extends over few
millimeters and in stem over a few centimeters.
3. Cell Maturation Phase
§ This lies behind the region of elongation.
§ Thickening of cell wall takes place.
§ The enlarged cell are modified into permanent tissues.
§ The mature cells then start to perform their different
functions.
Conditions for Growth (Factors)
There are different
factors which influenced the rate of growth and development.
These factors are
1. External Factors
2. Internal Factors
1. External Factors
External factors which influenced growth are
i. Temperature
ii. Light
iii. Oxygen
iv. Carbondioxide
v. Nutrients
i. Temperature
§ It is a very important factor.
§ All hormone and enzymes work optimumly in between 25oC to 37oC.
§ All metabolic functions of cell take place in between 0-35oC
range of temperature.
§ Normally, rate of growth increased with the increase of
temperature but within limit.
§ At very high temperature 35-40oC, the rate of growth stops and
plant dies.
ii. Light
§ Light is very important condition for the plant growth.
§ It helps in photosynthesis e.g. manufacturing of plant’s food.
§ Light affect the growth in three ways.
a. Light Intensity
b. Quality
c. Duration
a. Light Intensity
§ It affects the synthesis of chlorophyll and other pigments.
§ High light intensity destroys the chlorophyll.
§ Photosynthesis is reduced due to high light intensity.
b. Light Quality
§ Light quality also influence on growth rate.
§ Red light increase cell growth, blue light enhanced cell
division but ultraviolet light destroy the protoplasm and retards growth.
c. Light Duration
§ Duration of light affects the growth of vegetative and
reproductive structures.
§ It induced or suppressed the flowering.
iii. Oxygen
§ Oxygen influences the growth of roots.
§ Process of respiration is carried out in the presence of oxygen.
§ Without O2 no metabolic activity is possible and no growth takes
place.
§ High supply of O2 inhibits growth by photorespiration.
iv. Carbondioxide
§ CO2 is necessary for photosynthesis i.e. food production.
§ High concentration of CO2 retards growth.
§ Low concentration slows the process of photosynthesis.
v. Nutrients
§ Nutrients supply energy to growing plants.
§ With the increase in nutrition, growth increases where as
decrease in nutrition causes retardation of growth.
2. Internal Factors
Internal factors that effect growth are
i. Hormones
ii. Water
iii. Vitamin
iv. Genetic
Constitution
i. Hormones
§ In growth certain hormones play a very important role.
§ Plant hormones that influence growth are auxin, gibberellin and
cytokinin.
§ Deficiency of hormone causes growth retardation.
ii. Genetic Constitution
§ Genes influence growth.
§ Change in gene may cause alternation in hormone production and
certain process necessary for plant growth.
GROWTH CORRELATIONS
Definition
The growth of a plant organ is related with the growth of other organ
which takes place in different directions, this reciprocal relationship is called
as Growth Correlations.
Apical Dominance
Apical dominance is
the most important correlation found in plant. It is observed that during
growth of apical bud, growth of lower axillary bud is suppressed. When apical
bud is removed the growth of axillary bud is initiated.
Role of Auxin
Auxin is
responsible for apical dominance and also responsible for inhibiting the growth
of lateral bud.
Inhibitory Effect
The inhibitory of growth of lateral bud is called inhibitory effect.
Compensatory Effect
The removal of apex releases the lateral buds from apical
dominance is called Compensatory Effect.
Role of Cytokinin
Cytokinin also play
important role in apical dominance and in many cases if cytokinin is applied
directly on the inhibited but it allows lateral buds to be released from apical
dominance. Those plants that have dense growth have very little apical
dominance.
Growth and Development in Animal
Animals begin their
lives as single diploid cell called Zygote formed by the fusion of sperm and
ova. Development of zygote into adult involves a series of stages, which may
varies in different animals however the main stages are basically similar in
all. A broad outline of early stages of an animals embryonic life can be
represented as
1. Gametogenesis
2. Fertilization
3. Cleavage
4. Gasrulation
5. Organogenesis
6. Growth
1. Gametogenesis
The process of gamete formation is called gametogenesis.
Ova and sperm are formed in Gametogenesis.
2. Fertilization
Ova and sperm are fuse together to form a diploid nucleus
is called Fertilization.
3. Cleavage
Series of mitotic cell division to produce blastomeres is
called Cleavage.
4. Gastrulation
Arrangement of cells into three germinal layers is called
Gastrulation.
5. Organogenesis
The process in which body organs are form, cell interact
and differentiate is called Organogenesis.
6. Growth
Increase in the size of organs to attain maturity is
called Growth.
Development of Chick
The study of
development of chick provides a basis for understanding the early differentiation
of the organ system and the fundamental process of body formation, which is
common to all vertebrates.
Structure of Egg
The structure of
hen’s egg are as follows
Polylecithal Type
The egg of a hen is polylecithal type. In this egg,
enormous amount of yolk is present which is used as energy during the process
of development.
Primary Oocyte
When the egg is covered by a thin membrane called
Vitelline membrane.
Animal Pole
Its upper part is called animal pole.
Blastodisc
The protoplasm is restricted to a very small area called
Blastodisc or Germinal disc.
Secondary Oocyte
Primary oocyte become mature after releasing from the
ovary is called Secondary Oocyte.
FERTILIZATION
Definition
The process of fusion of sperm
with the ovum to form a single diploid cell, zygote is called fertilizatoin.
§ In hen, fertilization is internal.
§ It occurs in oviduct
§ After fertilization, second maturation division in secondary
oocyte to become mature ovum.
§ When ovum passes through the oviduct, it is covered by Albumen.
§ On the outer region of albumen two membranes are present known
as shell membrane.
§ The egg is covered by a hard porous, calcareous shell.
§ Fertilized egg is laid 24 hours after the fertilization.
Incubation
The fertilized ovum requires an optimum temperature
36-38oC for development. It provide either naturally by mother’s body or
artificially in incubator. At this temperature the chick completes development
and is hatched on the 21 days.
Phases of Development
The hen’s egg
undergo following phases during development
1. Cleavage
2. Morula
3. Blastula
4. Gastrula
5. Notochord Formation
6. Neuralation
1. Cleavage
The device of repeated mitolic divisions that takes place
in the fertilized ovum is called Cleavage.
Types of Cleavage
There are two types of Cleavage
i. Discoidal
Cleavage
ii. Meroblastic Cleavage
i. Discoidal Cleavage
The process of cell division is continued to the small
disc of protoplasm lying on the surface of the yolk at the animal pole. This
type of cleavage is called as Discoidal Cleavage.
§ It occurs in birds
ii. Meroblastic Cleavage
The type of cell cleavage in which blastodisc divide
completely is called Meroblastic Cleavage or incomplete cleavage.
§ It occurs in Fishes and reptiles.
§ The first two cleavage are vertical and the third runs
horizontal parallel to the surface as a result 8 blastomeres are formed.
§ The successive cleavages become irregular and number of cells
increase. This complete body is called Blastoderm.
2. Morula
Defintion
Cleavage results in the formation of a rounded closely packed mass of
blastomeres called Morula.
§ It is without cavity.
§ It consists compactly arranged cells called blastomeres.
§ Morula is short stage, very soon it is converted into blastula
stage.
3. Blastula
Definition
The embryonic stage which contains a fluid filled cavity, the
segmentation cavity or blastocoel is called Blastula.
§ By the appearance of cavity the cells of bolstoderm divide into
two layers.
i. Epiblast
ii. Hypoblast
i. Epiblast
§ The upper layer is called Epiblast.
ii. Hypoblast
§ The lower layer is called Hypoblast.
§ Between these two layers blastocoel is present.
a. Area Opaca
The marginal cells of blastoderm lie unseparated from the
yolk and form the zone of function called Area Opaca.
b. Area Pellucida
The middle or central region of balstoderm is called Area
Pellucida.
§ Egg is laid almost at this stage.
4. Gastrula
Definition
The embryonic stage in which movement and rearrangement of cells at
definite location in the embryo occurs is called Gasrula and the process of
formation gastrula is called Gastrulation.
In this stage, cell
begins to differentiate into definite layer which are
i. Endoderm
Formation
ii. Mesoderm Formation
iii. Ectoderm Formation
i. Endoderm Formation
§ Endoderm is formed from lower layer hypoblast of blastoderm.
§ Cells of area of pellucida (hypoblast) rearrange and migrate to
the lower region and spread over the yolk to form floor of sub-germinal cavity.
§ This newly form layer called endoderm, which consists of yolk
and stalk.
§ Stalk connects yolk region to embryo.
§ Invagination and archenteron are not formed in this type of
gastrulation.
ii. Mesoderm Formation
§ Mesoderm is middle layer and is produced from upper region of
blastoderm called Epiblast.
§ Invagination of Epiblast does not take place.
§ The cells of epiblast move downward in the middle of blastodisc,
the separates and move inward towards the yolk.
§ The cells are migrated from both sides and form a thick central
line called primitive streak.
§ The upper end of primitive streak is swoolen called primitive
knot or Hensen’s node.
§ The cells of epiblast pass through primitive streak and move in
blastocoel cavity form both sides and form a new layer called Mesoderm.
§ Due to migration of mesodermal cells, from epiblast a groove is
development on the entire upper region of embryo called primitive groove.
iii. Ectoderm Formation
§ The remaining cells of epiblast after migration of mesoderm form
the surface layer called Ectoderm.
§ At the end of this stage, embryo consists of three germinal
layers.
5. Notochord Formation
After the formation of primitive streak, the cells of
Hensen’s node are migrated to the inner side and form a rod-like structure in
the middle region it is notochord. It lies below the neural plate.
§ Notochord is formed in emrbyo in 18 hours.
§ It develops into vertebral column.
Differetiation of Mesoderm
After 24 hours of incubation, the lateral plate of
mesoderm is differentiated into two types of layers
§ Somatic layer => Outer layer
§ Spianchnic layer => Inner layer
6. Neuralation
Formation of Neural Plate
§ After gastrulation, the ectodermal cells of middle part of
dorsal region divide rapidly to form a thick plate called a Neural Plate.
Formation of Neural Flods
§ This plate moves downward and its edges arise on both sides to
form two folds, known as Neural Folds.
Formation of Neural Tube
§ These folds move towards each other, unite in the middle and
produce a tube, known as Neural tube.
Neurula
At this stage the emrbyo become elongated and called neurula.
§ The upper part of neural tube helps in the formation of brain.
§ The remaining tube forms the spinal cord and its cavity called
the neurocoel.
AGING
Definition
The process in which cells start deterioration in their structure and
function and tissues of the body become older is called Aging.
OR
Negative physiological changes in the body of multicellular organism is
called Aging.
Gerontology
The science which deals with the study of aging is called Gerontology.
Sign of Aging
The following signs of old age may usually be observed.
§ Loss of hair pigmentation
§ Skin wrinkled
§ Development of small pigmented area in the skin of face and
arms.
§ Loss of memory
§ Fat deposition increases
§ Vision become poor
§ Body become weak
§ Decreased body immunity
§ Degenerative diseases appears
§ Pain in joints
Causes of Aging
There are many
causes of aging, but two causes are very important
1. Genetic Origin
2. Gene Mutation
1. Genetic Origin
According to scientist Hayflick and Paul head cells of
body can divide for a limited period. The cells undergo mitosis certain times.
When cells do not work properly, cell division decreased, the body become
affected. It is the main cause of aging and cell start die.
2. Gene Mutation
Due to certain reasons changes in the genes and DNA
replication is affected. This is called mutation. Some substances damage the
DNA and function of cell become less / weak, it causes aging.
Using Measures to Decrease Aging
Low fat diet, low impact exercises, aerobic are the factors which reduced
aging.
CELL DIFFERENTIATION
Definition
The cell of selection of activation of some genes by a cell (which are
not activated by the other cells of the embryo) is called cell differentiation.
Experiment
John Gurdon removed the nucleus from the unfertilized egg of frog. Then he
obtained nucleus from intestinal cell of a tadpole of the same species and
implanted it into the enucleated egg. This egg with this new nucleus, developed
into a complete frog. It indicates that there is no change in the genetic
information of separated cell of any other part and it is active according to
the genes.
Example
Only in immature R.B.C the genes become active to form haemoglobin, so it
indicates the process of cell differentiation.
Mechanism of Differentiation
§ During the differentiation process, the genetic expression is
influenced by the cytoplasmic chemical composition.
§ Different properties of cytoplasm in the unfertilized ovum is
responsible for later differentiation of embryonic cells into tissues.
§ When cleavage occur in zygote, the cytoplasm is also divided.
§ Each dividing cell contain all necessary material like protein,
mRNA and other molecule.
§ With the help of these substance cell are changed into different
tissues.
EMBRYONIC INDUCTION
Definition
An embryonic tissue influences upon the other embryonic tissue through transmitted
some chemical stimulus. This phenomena is called Embryonic Induction.
EXPERIMENT OR MECHANISM OF EMBRYONIC
INDUCTION
Introduction
Hans Spemann, a classical embryologist, who got Nobel
Prize in 1935 performed an experiment of embryonic induction in 1924.
Experiment 1
Han Spemann separated the tissue frm presumptive nervous system present above
the nerve cord and transplanted into the belly region of the embryo.
Conclusion
He observed that these tissues of nervous system failed to develop at ectopic
site.
Experiment 2
In another experiment, they separate the presumptive notochord tissue and then
transplanted into presumptive belly ectoderm.
Conclusion
Nervous tissues started germination and they developed into neural tissues.
Result
From these experiments they concluded that an embryonic tissue influence upon
the other embryonic tissue through transmitting some chemical stimulus the
primary organizer. They help in embryonic induction.
REGENERATION
Definition
The ability to regain or recover the lost or injured part of the body
is called Regeneration.
Regeneration in Invertebrates
Regeneration is
very common in most of the invertebrates, such as Sponges, Coelentrates,
Pranarians, Annelids, Nematodes, Molluscans, Arthropods and Echinoderms.
In hydra a small piece of the body can be changed into a complete animal. In
earthworm and planaria when the body divides into two or more fragments each
fragment can develop into a new animal.
Regeneration in Vertebrates
In vertebrates many
groups have the ability of regeneration for example Salamander and Lizard
regenerate their limb and tail. Birds and Mammals have very poor regenerative
ability. In human the skin has this capability.
Abnormal Development
Deviation in the normal structure and functions of an organisms occur under
favourable conditions during embryological development are called abnormal
development. The study of such abnormalities is called Teratology.
Causes
The main reasons for the abnormal development are as follows
Mutation
Change in number of chromosome
Ultra voiled rays
Strong medicines
Abnormal functioning of certain glands.
Following are the
some abnormal conditions in human
i. Microcephaly
In this condition, individual with very small skull are born.
ii. Clef Lip and Palate
Upper lip has a cleft and there is a gap between the
palate.
iii. Polydactyle
Number of digits exceeds normal number.
iv. Dextrocardia
Heart towards the right side of the chest.
v. Sickle Cell Anemia
R.B.C become sickle shaped due to abnormality.
vi. Turner’s Syndrome
Female sexual defect in which there is one less sex
chromosome.
vii. Klinefelter’s Syndrome
Male sexual defect in which one more sex chromosome is
present.
viii. Down’s Syndrome
Mental and physical retardation
ix. Haemophilia
Decreased ability of the blood to clot.
x. Thalassemia
Formation of fragile (weak) R.B.C which break down and
cause haemolytic anemia.
Role of Cytoplasm in Development
Cytoplasm is also
important of embryo. To show the importance of cytoplasm experiment was
performed on frog’s embryo.
Experiment
The unfertilized
egg of frog has an upper pigmented half and a lower non-pigmented yolk half.
After fertilization a third region called Gray Crescent appears just opposite
to the point of entry of the sperm. As a result of first cleavage the embryo
divides into two daughter cells each receiving exact half of the Gray Crescent.
When the two daughter cells were separated each grow into normal tad pole
larva. In experiment Has Spermann separated the two cell in such a way that one
cell received all the Gray Crescent and the other cell got none. It was seen
that only that ceil developed into tadpole which had the cytoplasm from the
Gray Crescent while the other turned into undifferentiated mass of cells while
later died.
Conclusion
It can be concluded
that although both cells had similar genes, cytoplasm of both was different.
This shows that cytoplasm has some regulatory effect on the expression of
genes.
Role of Nuclues in Development
Nucleus is a part of
cell which acts like a brain. It also play an important role in reproduction.
The role of nucleus in regulating the activities of cytoplasm was studied in a
unicellular alga.
Experimental Material
Hamerling used alga
plant named Acetabularia, which has a long stalk and at the tip a cap like
structure. The cap is of two types one is umbrella shaped and another is
irregular-shaped. The nucleus is present in the lower region of the plant.
Experiment
When caps of both
types were removed each plant again produced cap of its own type. When cap and
stalk were grafted on the bases of the plant of other types. In this experiment
it was observed that each type produced the cap of its own shape inspite of
having separate-stalks.
Conclusion
Hence it is
concluded that the development of cap was regulated by the nucleus rather than
the cytoplasm.
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